Electric rectifier



April 3, 1934. H SIMON ET AL 1,953,781

ELECTRIC RECTIFIER Filed May 26, 1928 Inventors: Hellrnut Simon, max Barelss,

Their Attorney.

Patented Apr. 3, 1934 UNITED STATES 1,953,781 ELECTRIC RECTIFIER Hellmut Simon, Berlin-Friedenau, and Max Bareiss, Berlin-Charlottenburg, Germany, assignors to General Electric Company, a corporation of New York- Application May 26, 1928, Serial No. 280,87? In Germany July. 28, 1927 4 Claims.

The present invention comprises improvementsin rectifiers for alternatingcurrents and it is the object of the invention to improve the life and efiiciency of operation of such devices. Our invention is applicable particularly to the class of rectifiers which contain a thermionic cathode and a gaseous filling, such as a rare gas or mercury vapor, which becomes ionized during operation and increases the current-carrying capacity of the rectifier. The use of the gas, however, is accompanied by certain limitations in the operation of the device. For example, uncontrollable and undesired discharges are more apt to occur in a rectifier in the presence of gas and ordinarily the operation of such gasfilled rectifiers becomes more subject to arcing of a damaging character when the operating voltage becomes as high as several hundred volts. In some cases when the cathode is coated with a highly active thermionic material, the arcingback tendency of the rectifier is increased by the transfer of activematerial from the cathode to the anode. On the other hand, the electron emissivity of the cathode is apt to be decreased iby the deposition of vaporized anode material on the cathode.

These difficulties are particularly aggravated in a rectifier containing a plurality of anodes. In such a device there is impressed during operation a higher operating voltage between the anodes than between the cathode and any one of the anodes, thus favoring the flow of a leakage current in the gas which causes anode disintegration. In accordance with our invention these difficulties are overcome by the provision of a shield between the cathode and. the anode or anodes which is so constructed that little or no obstruction is afforded to the passage of an electron current whereas the physical transfer of material between the cathode and any of the anodes is substantially prevented.

In accordance with another feature of our invention reverse arcing is suppressed by constructing the anode, or anodes, of a material of poor electron emissivity, such as chromium, and in particular chromium having an oxidized surface.

The novel features of our invention will be more fully understood from the following specification taken together with the accompanying drawing in which Fig. 1 shows in perspective a rectifier embodying our invention, the bulb being in part broken away; Fig. 2 is a vertical section of the electrode structure of Fig. 1; and Fig.

3 is a perspective view of the electrode structure of a modification;

The rectifier showninFig. 1 comprises a bulb or envelope 1, consisting of glass or .the like and havingzmounted therein a thermionic cathode 2 shown in an elongated form and anodes 3, 4. The bulb contains a rare gas, or a vapor, such as mercury vapor at suitable pressure, say 100 microns or more sufficient to support a glow discharge. A discharge of this sort differs from a discharge in a high vacuum by the fact that it is not limited by space charge. The cathode may consist of nickel or other suitable metal provided with a coating of thermionically active material, such as barium oxide, or other alkaline 710- earth oxide. Tungsten containing thoria also may be used as cathode material. The cathode is connected as usual to sealed in conductors 5, 6. The anodes preferably consist of chromium or of other metal coated with chromium. The surface of the anodes preferably is oxidized. The anode conductors 7, 8 are surrounded by insulating sleeves 10 and 11 which may consist of alumina, thoria or similar refractory material. A trough-shaped shield 12, which may consist of nickel or molybdenum is supported by a wire 13 so as to partly surround the cathode. This shield is imperforate so as to intercept materials projected from the cathode to the anodes or vice versa but openings extending the length of the cathode are left at the top and the ends as indicated, which are out of line of the path of such projected materials but otherwise provide for the unobstructed passage of current between the electrodes.

The shield preferably is connected to the cath ode by a wire 18, as shown inv the drawing.

Fig. 3 shows a somewhat modified structure in which the anode sleeves 10, 11 are omitted and the cathode 15 is arranged in a substantially upright position, the shield 16 having its main' opening at one side out of direct line with the anodes 3, 4, but providing a circuitous path for the passage of current. The support 1'7 for the shield is led through the stem 14 so as to permit of desired electrical connection externally.

Our invention is not restricted to discharge devices containing anodes consisting of chromium. However, when ordinary metal, such as tungsten or tantalum, are used as anode materials, the impurities or oxides contained therein should be carefully removed. For example, it is desirable to use metals melted in a high vacuum or to heat the anodes in a completed tube by means of the discharge to such extent that incipient fusion occurs thereby completely purifying the anode metal.

If highly oxidizable substances, such as calcium and magnesium, are used to obtain a high vacuum initially or to maintain the gas purity, then the shield about the cathode may also serve the purpose of preventing volatilization of such metals upon the anode. With this purpose in view the calcium, or the like, may be applied to the cathode or current conductor where during volatilization thereof the anodes will be shielded from the vapor emanations.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric rectifier comprising a container, cooperating electrodes therein including a thermionic cathode and an anode, a gaseous filling, and a cylindrical shield closely adjacent to and partially surrounding said cathode, also electrically connected to the latter, said shield being interposed in the direct path from the cathode to the anode and having an elongated opening which offers an unobstructed circuitous path between said electrodes.

2. An electric rectifier comprising an envelope,

an attentuated gas therein, a thermionic cathode, a plurality of anodes, and a solid cylindrical metallic shield located closely adjacent said cathode and being electrically connected thereto, said shield having an opening which extends the length of the cylinder and is out of line with said anodes.

3. An electric rectifier comprising a container, cooperating electrodes therein including a thermionic cathode, a gaseous filling, and a cylindrical shield closely adjacent to and partially surrounding said cathode, also electrically connected to the latter, said shield being open at both ends and interposed in the direct path from the cathode to a cooperating electrode but leaving unobstructed a circuitous path between the cathode and said electrode.

4. An electric rectifier comprising an envelope, an attenuated gas therein, an elongated thermionic cathode, a plurality of anodes, and a solid cylindrical metallic shield located closely adjacent said cathode and being electrically connected thereto, said shield having an opening extending the entire length of the shield.

HELLMUT SIMON. MAX BAREISS. 

